COFFEE
James Hoffman: https://www.youtube.com/channel/UCMb0O2CdPBNi-QqPk5T3gsQ
Deep dives into coffee machines, grinders, techniques, beans, roasting, etcetera with a healthy dose of scientific discipline to each.
Lance Hendrick: https://www.youtube.com/c/LanceHedrick
As above, only WAY more detail. Sometimes more than you need. I found his reviews of low-priced (yet high quality) coffee grinders to have almost too much detail, but when I slogged through it I eventually worked out the perfect grinder for my needs and only ended up spending around $300-400, which frankly is amazing.
FOOD
ThatDudeCanCook: https://www.youtube.com/c/CookingwithSonny
High end chef techniques that are explained in impressively accessible detail. My only problem with this channel is I now am always disappointed when I order steak out anywhere because I know I can cook it SO MUCH BETTER MYSELF. If you take nothing else from this list, watch his video on cooking filet mignon: https://www.youtube.com/watch?v=fDrkI9_EEe8 If you follow the technique your mind will be blown.
How to Cook That: https://www.youtube.com/c/HowToCookThat
Food scientist esoteric cooking techniques, ingredients, weird stuff, and quite mind-blowing investigations into the Russian content factories that pump out fake "5 minute life-hack" media.
Chinese Cooking Demystified: https://www.youtube.com/c/ChineseCookingDemystified
American + Chinese couple living in Guangdong exploring authentic Chinese regional specialties. They do a great job of explaining the techniques and testing realistic alternatives for the more obscure ingredients that are simply unavailable outside of China.
Blondie in China: https://www.youtube.com/c/BlondieinChina
Aussie girl fluent in Mandarin, living in and exploring China's regions, cuisines and discovering all the things about day-to-day life that we just don't see from outside. Always entertaining, informative and interesting.
Tasting History: https://www.youtube.com/c/TastingHistory
Recreating famous dishes from history and taste-testing them, with detailed backgrounds of the why, where, how, when and who for each.
Xiao Ying Cuisine: https://www.youtube.com/channel/UCJJDD-Hy76jvUMRG-dpFkcw/fea...
New recipes almost every day. Dunno who she is, but they're always interesting dishes and mostly stuff I've never seen elsewhere.
SCIENCE/NERDY STUFF
Up and Atom: https://www.youtube.com/c/UpandAtom
Physics, Quantum theory, Maths.
Tom Scott: https://www.youtube.com/c/TomScottGo
Really hard to categorise, but he does a great job exploring all manner of obscure things in detail.
Julian O'Shea: https://www.youtube.com/c/JulianOShea
Industrial design, architecture, city planning, Melbourne, obscure stuff.
HARDWARE
Jeff Geerling: https://www.youtube.com/c/JeffGeerling
Great projects in and around the Raspberry Pi, Arduino, maker electronics spaces.
MUSIC
Dub Monitor: https://www.youtube.com/c/DubMonitor
Far too much detail about Dub Techno, minimalist techno.
VISUAL
Max Cooper: https://www.youtube.com/c/MaxCoopermax
Thought-provoking and mind-bending visuals and excellent music.
Max Hattler: https://www.youtube.com/user/maxhattler
Not that active any more, regrettably. But similar to above. What is it with people called Max and visuals?